1. Field of the Invention
The present invention relates to a biosensor and method for bone mineral density measurement, which can monitor changes in bone mineral density (BMD) by detecting the content of tartrate-resistant acid phosphatase (TRAP) in blood.
2. Description of Related Art
Osteoporosis is one of the most common chronic illnesses among the elderly people. Statistics shows that osteoporosis hits approximately 20 million people and is the cause of about 1,300,000 fracture incidents in the United States each year. Treatment of fracture increases medical expenses to the tune of about US$14 billion a year. Japan is a geriatric society with a population of 120 million people, and about 5 million of which are afflicted with osteoporosis and potential patients may be as many as 10 million. Taiwan has a population of 20 million people. More than 30,000 people who suffer from fracture of femur each year could be attributed to osteoporosis, and 5% to 25% of those patients died of fracture-related complications.
Bone mineral density peaks in the age of 30 in both men and women and declines gradually thereafter. If no preventive action is taken, signs of osteoporosis will appear in the age of 40, particularly in women. What should be noted is that this disorder begins without any symptoms. For women over the age of 50 who are in menopause, the loss of bone mass accelerates. Related symptoms of osteoporosis begin to surface in patients over age 60 or are manifested directly in fracture.
Normal bone tissue carries on the process of formation and resorption continuously through the actions of osteoblasts and osteoclasts to maintain the balance of bone mineral density. But when osteoclasts become more active than osteoblasts, bone fracture, which is a bone resorption disorder, tends to occur. There are two kinds of bone resorption disorder: First, osteoporosis commonly presented in post-menopausal women, elderly people and people on steroid therapy; second, bone disorder caused by hyperparathyroidism. When osteoporosis-related fracture occurs, the bone mineral density in the patient is typically 60˜70% or lower of that in normal people at their peak. At this time no effective and safe regimen is available to restore the bone mineral density. The condition of the patient can only be kept from deteriorating. Thus prevention of osteoporosis is very important.
Commonly used techniques for measuring bone mineral density include bone puncture, DEXA (dual energy X-ray absorptionmetry), and sonography. Bone puncture is an accurate but invasive procedure, which involves the extraction of bone mass from spine area. This procedure carries risk and is not well accepted by patients. DEXA is the main device used by the hospitals to measure bone mineral density (BMD). In DEXA, two low-dosage x-ray beams with differing energy levels are aimed at the patient's spine, hip or whole body. The computer calculates the content of BMD based on the fact that different bones absorb different energy levels. DEXA is also highly accurate. But the apparatus is bulky and expensive and emits radiation. The US FDA has approved a few products that use sonography to measure BMD. Such devices measure the BMD of peripheral bones, such as heel, shin bone and kneecap. But the BMD in spine or hip change faster than that in heel, shin bone or kneecap. Thus sonography is not as accurate or sensitive as DEXA in the determination of BMD. DEXA allows early detection of abnormal change in bone mass for its targets spine, hip or whole body. But sonography offers the advantages of low cost and radiation-free.
Tartrate-resistant acid phosphatase (TRAP) is an enzyme secreted by osteoclasts. Its activity or concentration has been shown to have relations with the rate of bone resorption and formation. Thus TRAP in blood is often used as an index of bone resorption and formation rate and applied in the monitoring of BMD. There are two forms of TRAP: TRAP 5a and TRAP 5b, of which TRAP 5b is a more meaningful index. The U.S. Pat. No. 6,248,544 discloses an immunoassay for measuring the level of TRAP and defines its activity by spectrophotometer to determine bone resorption and formation rate, and based on which to diagnose osteoporosis disorder or monitor the prognosis of osteoporosis treatment. However the immunoassay provided is time consuming that does not allow quick test.
In summary, there is a need to develop small-sized biosensor that allows quick testing and easy reading of BMD to facilitate the monitoring of bone mass change and prevention of osteoporosis.